Integrated focusing emitter

ABSTRACT

A method for creating an electron lens includes the steps of applying a polymer layer on an emitter surface of an electron emitter and then curing the polymer layer to reduce volatile content.

This application is a divisional of application Ser. No. 09/881,981,filed Jun. 14, 2001, herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to the fabrication of lens design forelectron emitters, particularly those electron emitters used in massstorage and display devices often incorporated in many electronicdevices.

Computing technology continues to become less expensive while providingmore capability. To allow computing technology to continue thesepositive trends, peripheral devices such as mass storage devices anddisplay devices must continue to advance. Much criticism has been voicedin the trade press about the lack of mass storage devices such as diskdrives, CD-ROMs, and DVD drives, to name a few, to increase their datarates up with the advancing speed of the microprocessors found incontemporary personal computers. However, hard disk drives, for examplehave been able to increase their storage density tremendously over thelast decade but are now encountering physical limitations that preventsfurther progress in this area. Display devices, such as LCD monitorshave had difficulty in fulfilling demand due to the complexity ofmanufacturing them with near-zero defects. Further, the use of passiveLCD technology has required the addition of backlights to allow forviewing in different ambient light conditions thereby adding cost andincreasing power requirements.

Electron beam technology has been present for many years in consumerproducts such as television (TV) tubes and computer monitors. Thesedevices use what is known as “hot cathode” electrodes to create a sourceof electrons that are directed to and focused on the viewing screen.While research has taken place in a number of new technological fieldswith emission devices, the field of “cold cathode” electron emitterssuch as Spindt-tips and flat emitters has attracted the attention ofmany manufacturers.

Several problems exist in converting this cold cathode technology toproducts. One such problem is the creation of an electron focusingstructure that can be used in multiple applications that require a highdensity of cold cathode emitting devices such as with mass storage anddisplay devices. Conventionally, dielectric materials are used as spacermaterial between the electron focusing structure and the electronemitter. However, the cost and complexity of building the electronfocusing structure with dielectric material hinders the rapiddevelopment of new products using cold cathode technology. In order tofurther the introduction of new products using cold cathode technology,more cost effective and simpler processes for building electron focusingstructures and ultimately the mass storage and display devices areneeded.

SUMMARY OF THE INVENTION

A method for creating an electron lens includes the steps of applying apolymer layer on an emitter surface of an electron emitter and thencuring the polymer layer to reduce volatile content.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is better understood with reference to the followingdrawings. The elements of the drawings are not necessarily to scalerelative to each other. Rather, emphasis has instead been placed uponclearly illustrating the invention. Furthermore, like reference numeralsdesignate corresponding similar parts, though not necessarily identical,through the several views.

FIG. 1A is a top view of an exemplary embodiment of an integratedfocusing emitter.

FIG. 1B is a cross-sectional view of the exemplary embodimentillustrated in FIG. 1A.

FIG. 2 is an exemplary cross-sectional view of an alternative embodimentof an integrated focusing emitter with a direct tunneling emitter.

FIG. 3 is a perspective view of an exemplary embodiment of a displaydevice that incorporates the invention.

FIG. 4 is a cross-sectional view of an alternative exemplary embodimentof a display device that incorporates the invention.

FIG. 5 is a perspective view of an exemplary embodiment of a massstorage device that incorporates the invention.

FIG. 6 is a cross-sectional view of an alternative exemplary embodimentof a mass storage device that incorporates the invention.

FIG. 7 is a block diagram of an exemplary process used to create anintegrated focusing emitter including the steps to create an electronlens that incorporates a polymer spacer layer.

FIGS. 8–14 are illustrations of exemplary process steps to create anelectron emitter that provides a base for the electron lens of theinvention.

FIGS. 15–16 are charts that illustrate exemplary temperature profilesfor alternative annealing processes used to create an electron emitter.

FIG. 17 is an illustration of the application of a polymer layer to theelectron emitter base.

FIG. 18 is a chart of an exemplary curing process used to extractvolatile content from the polymer layer shown in FIG. 17.

FIG. 19 is an illustration of the deposition of a conductive layer onthe polymer layer.

FIG. 20 is an illustration of the masking and etching of the conductivelayer of FIG. 19 to create an electron lens opening.

FIG. 21 is an illustration of the result of a selective etching processthat etches the polymer layer to expose the electron emitter surface.

FIG. 22 is an illustration of the result of a deposition of a emittercathode layer to finish creating the integrated focusing emitter.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATIVE EMBODIMENTS

To reduce costs and allow for reduced processing steps, the inventionincorporates using a polymer layer as spacer material between theelectron emitter and the focusing lens thereby creating an integratedfocusing lens. To allow for incorporation of a polymer spacer layerseveral problems must be overcome.

First, polymer material generally has volatile components that canoutgas over time. This outgassing can be a concern when the electronemitter is operating in a vacuum, typically less than 10⁻⁵ Torr of airpressure. The outgassing of polymer material can affect the air pressurelevel, thus requiring an active vacuum pump or getter material to removethe release volatile contents. Further, if the volatile contents of thepolymer are released into the vacuum during operation, an emittedelectron can strike a portion of the volatile content and ionize it. Ifthere is a large voltage potential between components in the devicesincorporating the electron emitter, the ionized volatile componentaccelerates toward the cathode of the emitter and collides with it,thereby causing damage. Thus, it is customary to use spacer materialthat does not outgas. The invention includes a curing process for thepolymer material that reduces significantly the volatile contents of thepolymer material such that a vacuum of less than 10⁻⁵ Torr can bemaintained without active vacuum pumping.

Second, because of the material interface characteristics, high stressinterfaces can exist between a polymer spacer material and theconductive material used to create the electron lens. A high stressinterface can result in rough surfaces and cracks in the conductivematerial that might affect the performance of the electron lens. Theinvention includes using preferably a substantially gold material forthe conductive layer used for the electron lens.

Third, because the polymer material is etched by using the opening inthe conductive layer for the electron lens as a mask for etching polymermaterial, the etching process preferably accounts for an etch profilewith minimal undercutting under the conductive layer that is used forthe electron lens. Too much undercutting causes the conductive layer tonot have adequate support and might cause the electron lens to becomedeformed and not operate properly.

Fourth, the etching process for the polymer material must notsignificantly etch the conductive layer used for the electron lens orleave residue from the etching process on the emitter surface. Anymaterial on the emitter surface, such as traces of the conductive lenslayer or polymer material can affect the performance of the electronemitter by changing its emission characteristics.

Fifth and most important, the etch selectivity of the polymer etchprocess is important so as to not significantly etch the emitter surfacewhich can damage the electron emitter. Thus, the etch process of theinvention balances the etch conditions to trade off etch rate, etchresidue, etch selectivity of the conductive lens layer, etch selectivityof the emitter surface, and etching power used. By choosing the properparameters, an etch selectivity between the polymer and the emittersurface greater than 1000:1 is achieved.

More aspects of the invention will become apparent in the followingdescription of preferred and alternative embodiments of the invention.The semiconductor devices of the present invention are applicable to abroad range of semiconductor device technologies and can be fabricatedfrom a variety of semiconductor materials.

The following description discusses several presently preferredembodiments of the semiconductor devices of the present invention aspreferably implemented in silicon substrates, since the majority ofcurrently available semiconductor devices are fabricated in siliconsubstrates and the most commonly encountered applications of the presentinvention will involve silicon substrates. Nevertheless, the presentinvention may also advantageously be employed in gallium arsenide,germanium, and other semiconductor materials. Accordingly, the presentinvention is not intended to be limited to those devices fabricated insilicon semiconductor materials, but will include those devicesfabricated in one or more of the available semiconductor materials andtechnologies available to those skilled in the art, for example,thin-film-transistor (TFT) technology using polysilicon on glasssubstrates.

It should be noted that the drawings are not true to scale. Further,various parts of the active elements have not been drawn to scale.Certain dimensions have been exaggerated in relation to other dimensionsin order to provide a clearer illustration and understanding of thepresent invention.

In addition, although the embodiments illustrated herein are shown intwo-dimensional views with various regions having depth and width, itshould be clearly understood that these regions are illustrations ofonly a portion of a device that is actually a three-dimensionalstructure. Accordingly, these regions will have three dimensions,including length, width, and depth, when fabricated on an actual device.Moreover, while the present invention is illustrated by preferred andalternative embodiments directed to active and electronic devices, it isnot intended that these illustration be a limitation on the scope orapplicability of the present invention. It is not intended that theactive and electronic devices of the present invention be limited to thephysical structures illustrated. These structures are included todemonstrate the utility and application of the present invention topresently preferred and alternative embodiments.

FIG. 1A is a top view of an exemplary embodiment of the invention thatintegrates an electron lens and preferably, but optionally, anelectrostatic shield, with an electron emitter. In FIG. 1A, the electronemitter 20 emits electrons that are focused using a co-planer electronlens 16 having a lens opening 18. The co-planer lens 16 is formed on aconductive layer and is held at a voltage potential relative to acathode surface of the electron emitter 20. The amount of voltagechosen, lens geometry, and distance from the electron emitter 20determines the amount of focus performed by the co-planer electron lens16. Optionally, on the same conductive layer as the co-planer lens 16 isa co-planer shield 14 that is held at a different voltage than theco-planer lens 16. Preferably, the voltage of the co-planer shield 14 isheld at about the same voltage as an anode target for the electron beamemitted by the electron emitter 20. The co-planer lens 16 is separatedfrom the co-planer shield 14 by a gap 22 to provide electricalisolation.

FIG. 1B includes a cross-sectional view of the focused emitter of FIG.1A along the I—I section. Also included is an anode 76 that is thetarget of the electron beam from electron emitter 20. The electronemitter 20 can be one of several types such as a direct tunnelingemitter, a metal-insulator-metal emitter, ametal-insulator-semiconductor emitter, an array of spindt tip emitters,or a single spindt-tip emitter to name a few. The electron emitter 20 isformed within and/or disposed on a substrate 10, preferably a siliconsubstrate but other substrates such as glass, germanium, or galliumarsenide, for example can be used instead and still meet the spirit andscope of the invention. Disposed on the substrate 10 is a polymer layer12 used as a spacer for the co-planer lens 16 and co-planer shield 14formed in a conductive layer. The electrons emitted by the electronemitter 20 are focused by an electric field formed within the lensopening 18 and are attracted to the anode 76 that is preferably held ata high positive voltage relative to the electron emitter 20. The anode76 is disposed an anode-lens distance 24 to achieve a focused spot onthe anode. If the lens design chosen is such that the anode-lensdistance 24 requires a small distance thereby creating a largeelectrostatic attractive force 26, then the co-planer shield layer 14 isoptionally used and held at about the same potential as the anode 76 toreduce the electrostatic force 26. If the anode 76 is held at aanode-lens distance 24 such that the electrostatic force 26 is weakenough for a given application, then co-planer shield 14 is notnecessary.

FIG. 2 is an illustration of an exemplary direct tunneling emitter thatincorporates an integrated electron lens of the invention to create anintegrated focusing emitter 60. In this embodiment, the substrate 10 ispreferably a silicon substrate preferably heavily doped. Substrate 10 isalternatively any other conductive material or substrate that provides asupply of electrons. On substrate 10 a stack of thin-film layers 38 isapplied or processed to create the direct tunneling emitter. A tunnelinglayer 30 is disposed on the substrate 10 and is preferably less than 500Angstroms, more preferably about 100 Angstroms. On the tunneling layeris disposed a cathode layer 36 of preferably a thin film of metal suchas about 50 to about 100 Angstroms of platinum, although other metalscan be used. For example, other metals include but are not limited togold, iridium, molybdenum, chromium, and tungsten. On the stack ofthin-film layers 38 is disposed a polymer layer 12 used to space theelectron lens 28 from the electron emitter. Preferably, the polymerlayer is between about 2 to about 12 micrometers thick or greater. Ananode 76 is disposed at a anode-lens spacing 24. The electron lens 28 isheld at a voltage potential relative to the cathode layer 36 and createsan electric field 34, which focuses the electrons emitted from theelectron emitter to create a focused beam 32. The electric field 34, thelens opening, and the anode-lens spacing 24 are chosen to provide adesired spot size on the anode 76.

FIG. 3 is a partial view of an embodiment of an exemplary display device70 that incorporates the invention. A cathode layer 78 has electronemitters 20 disposed or formed within that create an electron beam 50.Disposed on the cathode layer is a polymer layer 12 that further has alens layer 40 disposed on it. Formed within the lens layer 40 and thepolymer layer 12 are opening 42 that allow the electron beams 50 to exitand reach pixels 72 on the anode 76, preferably the display screen. Thepixels are preferably made up with phosphor material, either in amonochromatic or multiple color order, such as red, green, blue. Whenthe electron beam 50 reaches the pixels 72, the phosphor material isexcited by the electrons and emits photons that create visible light.

FIG. 4 is an alternative embodiment of an integrated display device 80that is illustrated in cross-section form. The integrated display device80 has a substrate 10, preferably a silicon substrate that is processedwith semiconductor processing to include a stack of thin-film layers 38that incorporate electron emitters 20. The electron emitters 20 createelectron beams 50 which are used to excite display pixel 84 made ofphosphorous material. Disposed on the stack of thin-film layers 38 is apolymer layer 12 that has openings to allow electron beams 50 to passthrough to lens layer 40 disposed on the polymer layer 12. The lenslayer 40 has openings for focusing the electron beam 50 onto the displaypixel 84. The display pixel 84 is formed within anode 86 that capturesany stray electrons. The display pixels 84 and anode 86 are disposed onthe display screen 82, preferably a glass or other transparentsubstrate. The anode 86 is spaced from the lens layer 40 by a spacer 88that is also preferably a hermetic seal. Optionally, an alternative seal86 is placed around the display to further provide a hermetic seal oradhesive joint between the display screen 82 and the substrate 10 withits stack of thin-film layers 38 and polymer layer 12.

FIG. 5 is a partial view of an exemplary embodiment of a mass storagedevice 90 that incorporates the invention. In this embodiment, the massstorage device 90 has at least three substrates, a substrate 10, a rotorsubstrate 92, and a stator substrate 94. The substrate 10 has a stack ofthin-film layers processed on it that contains active devices such aselectron emitters 20. Disposed on the stack of thin-film layers 38 is apolymer layer 12 that provides spacing for electron lens 28. Theelectron lens 28 creates a focused beam 32 that is used to read/writeinformation on the surface of media 96 on the rotor substrate 92. Themedia surface is preferably made up of a phase change material that canexist in either a crystalline or amorphous state depending on the timeand amount of energy expended on it by the focused electron beam. When alow power electron beam is used to read the crystalline or amorphousstate, electrons are detected in the rotor substrate 92 by a readercircuit 98. The reader circuit 98 includes an amplifier 95 that detectsthe current in the rotor substrate 92 between media contact 91 andsubstrate contact 97. When the focused beam 32 strikes an amorphous spot93 the amount of current which flows to the amplifier circuit isdifferent than when the focused beam 32 strikes a crystalline area.Preferably, a conventional digital media recording format is used torecord information in the media 96. To make an amorphous spot, ahigh-energy focused beam is presented to the surface of the media 96 fora short time and allowed to cool rapidly. To remove the amorphous spotand return the media 96 to a crystalline state, the amorphous spot 93 isheated with a high-energy focused beam 32 and allowed to cool slowly byslowly changing the energy of the focused beam 32.

FIG. 6 is an exemplary integrated mass storage device 100 thatincorporates the invention illustrated in cross-sectional form. Asubstrate 10 has a stack of thin-film layers 38 that incorporates theelectron emitters 20. Disposed on the stack of thin-film layers 38 is apolymer layer 12. Disposed on the polymer layer 12 is an electron lenslayer 28 used to focus electrons from electron emitters 20 into afocused beam 32. The substrate 10 and its stack of thin-film layers 32and polymer layer 12 are attached to a rotor substrate 92 using a spacer88 and seal 89 to provide an evacuated environment, preferably less than10⁻⁵ Torr. The rotor substrate 92 has a movable portion containing media96. The movable portion is attached to the rotor substrate 92 usingsprings 152, preferable formed and etched from rotor substrate 92 usingmicro-mechanical machining techniques. The rotor substrate 92 isattached to a stator substrate 94 by seal/adhesive 158. Electricalcontact is made by inter-substrate contacts 156. The stator substrate 94and the rotor substrate 92 control the movement of the movable portionof the rotor substrate 92 by the use of an electrostatic stepper motor154. The electrostatic stepper motor 154 is preferably movable in afirst and second direction but some embodiments may limit the movementto a single direction. By providing for movement of the media 96, eachelectron emitter 20 can read/write several locations on media 96, thusproviding for increased density of information storage. The polymerlayer 12 provides for separation of the electron lens layer 28 from theelectron emitter 20.

FIG. 7 is a flowchart of an exemplary general process used to create anintegrated focusing emitter including the steps to create an electronlens using a polymer spacer layer. These process steps can beimplemented with several different technologies for creating anintegrated focusing emitter using conventional semiconductor processingtechniques known to those skilled in the art. The integrated focusingemitter begins with the selection of a substrate, preferably silicon butother substrates are known to those skilled in the art and can besubstituted and still meet the spirit and scope of the invention. Thepurpose of the substrate is to provide a source of electrons and also toprovide a stable platform for further processing of a stack of thin-filmlayers that contain the electron emitter and also the processing of theintegrated electron lens.

In step 102, an isolation layer is created on the substrate with atleast one opening to define the location of the electron emitter such asby masking and growing or depositing dielectric materials. For a siliconsubstrate, the isolation layer is preferably field oxide growth (FOX) orother dielectrics such as thermal oxide, silicon nitride, silicondioxide, or silicon carbide to name a few. In optional step 104,depending on the isolation layer used, an adhesive layer such astantalum can be placed (disposed) on the isolation layer to allow forbetter adhesion of a first conductive layer that is applied in step 106.In step 108, the first conductive layer is patterned, preferably withphotoresist, to create an opening for the well of the electron emitter.In step 110, the first conductive layer is etched in the opening,preferably a wet etch to create an anisotropic profile although otheretch techniques can be substituted such as a dry etch. In step 112, theadhesive layer is preferably dry etched to create an isotropic profile.The etching of the adhesive layer is not performed of course if theoptional adhesive layer is not used or applied in step 104. In step 116,a tunneling layer is preferably deposited on the exposed substratesurface and on top of the pattern material used to create the opening inthe first conductive and adhesive layers. In step 118, preferably a liftoff process is used to remove the pattern material and to lift off thetunneling material that was disposed on the patterning material withoutremoving the tunneling material that is disposed on the substrate. Forpositive photoresist, the preferable lift off process uses an oxygen ashetch process.

In step 120 the processed substrate is subjected to an annealing processthat increases the emission current density of the electron emitter.

In step 122, the polymer layer is deposited on the processed substrate.Then is step 124, the process substrate with the polymer layer isconditioned by curing the polymer layer to remove volatile componentsand compounds from the polymer material. The actual curing process usedwill depend on the type of polymer material chosen. In step 126, asecond conductive layer is deposited on the polymer layer for use increating the electron lens and optional shield.

In step 128 the second conductive layer is masked and patterned tocreate the focusing lens. In step 130, the second conductive layer isetched within the pattern openings to create the lens opening. Then instep 132, a selective etch is performed on the polymer layer to thesurface of the electron emitter with preferably little undercut underthe electron lens. In step 134, a third conductive layer is depositedover the second conductive layer and within the lens opening on thesurface of the electron emitter to create a cathode layer on thetunneling layer of the electron emitter.

FIGS. 8–22 are exemplary illustrations of the processing of a substrate10, preferably a silicon substrate, to create an integrated electronemitter using specific embodiments of semiconductor processing steps.The process steps shown are by way of example to make clearer anunderstanding of the invention in a specific embodiment and are notmeant to limit the methods of making the invention.

FIG. 8 shows substrate 10 having a FOX-mask 44 patterned thereon todefine a location for the electron emitter surface. Preferably theFox-mask 44 is a hard mask such as a dielectric but also could be aphotoresist.

FIG. 9 shows the growth of the field oxide and the removal of theFOX-mask 44 from FIG. 8. The field oxide thickness is typically withinthe range of 3000–10,000 Angstroms.

FIG. 10 shows the application of an optional adhesive layer 48,preferably tantalum, on the FOX and emitter surface areas over thesurface of the substrate 10. Preferably the adhesive layer 48 is appliedusing a deposition process to a thickness of about 500 Angstroms.

FIG. 11 shows the application of a first metal layer 52, preferably goldon top of the adhesive layer 48. The preferred thickness of the firstmetal layer 52 is about 2000 Angstroms. If a first metal layer 52 ischosen that has good adhesion properties to the insulating layer chosenthen the adhesive layer 48 is not required.

FIG. 12 illustrates the results of etching of the first metal layer 52and the adhesive layer 48. To perform the etching, first a first metalphotoresist is applied on the first metal layer 52 and patterned todefine an opening where etching is to occur. The opening in the firstmetal photomask is preferably aligned over the emitter surface definedin the FOX material. The first conductive layer is preferably wet etchedto form an anisotropic profile in which the portion of the first metallayer 52 next to the first metal photoresist 54 is undercut from theopening. Optionally, a dry etch process can be used. If an adhesivelayer 48 is used, then the adhesive layer 48 is preferably dry etched toform an isotropic profile having substantially parallel side walls fromthe first metal layer 52 to the substrate 10 surface. The etching of thefirst metal layer 52 and the adhesive layer 48 creates the emitter well68.

FIG. 13 illustrates the result of a deposition of the tunneling layer 30on the processed substrate 10. The tunneling layer 30 is applied to anddisposed on the surface of the first metal photomask 54 and the exposedsurface of substrate 10 within the emitter well 68. Preferably thetunneling layer 30 is applied to a thickness of about 50 to about 100Angstroms using a high dielectric film such as TiO_(x), WSiN, TaAlO_(x),AlO_(x), AlO_(x)N_(y), and TaAlO_(x)N_(y), but preferably TiO_(x) toabout 100 Angstroms. Other possible dielectric films includesilicon-based dielectrics such as about 200 to about 500 Angstroms ofSiN and SiC. Other dielectrics that can be used to create a metalinsulator semiconductor emitter are known to those skilled in the art.

FIG. 14 is an illustration of a lift off process used to remove thefirst metal photoresist 54 and the tunneling layer 30 that is depositedon it. An oxygen rich ash etch is used to remove the first metalphotoresist 54 and the portion of the tunneling layer 30 on the firstmetal photoresist 54. Preferably the process used is directional enoughto not affect the portion of tunneling layer 30 disposed in the emitterwell 68.

FIGS. 15 and 16 are charts of temperature over time for alternativeannealing processes 140 and 142, respectively, used to increase theemitter current from the emitter. In FIG. 15 the processed substrate 10after the ash etch in FIG. 14 is raised to a temperature of 400 C withinabout 10 minutes and held there for about 30 minutes. Then, the processsubstrate 10 is slowly brought back to room temperature (about 25 C)over about 55 minutes. In FIG. 16, the processed substrate 10 is raisedfrom room temperature to about 600 C in about 10 minutes and held therefor about 30 minutes. Then the processed substrate 10 is slowly broughtback to room temperature over the course of about 100 minutes.

FIG. 17 illustrates the application of polymer layer 56 onto the stackof thin-film layer 38 on the processed substrate 10. The polymer layer56 is preferably applied using a positive photoresist such as novolacbased resist although it is anticipated that SU8 material would work.Preferably the resist is spin-coated to about 5.5 to about 6.5 micronsthick and baked on a contact hot plate at about 125 C for 2 min. Thethickness of the polymer material is determined by the lens design andcan range usually between about 2 microns and about 12 microns. Becausepolymer material may have volatile components, the preferred process isto perform a curing of the polymer material to remove most of thevolatile content.

FIG. 18 is a chart of an exemplary curing process to remove the volatilecontent from the polymer layer 56 material. The processed substrate 10with the applied polymer layer 56 is placed in an over and thetemperature is ramped up from room temperature (about 25 C) to 180 C inabout 1 hour. Then the polymer is cured at 180 C for about 4 hoursbefore the substrate is ramped down back to room temperature in about 1hour. The curing process is easily adjusted to account to optimize fordifferent polymer materials. Using this process with the novolac basedresist, empirical results show that a vacuum of 5×10⁻⁸ Torr can bemaintained using the polymer layer 56.

FIG. 19 illustrates the results of an application of a second conductivelayer 58 on the polymer layer 56 used as a lens layer. The interfacebetween the second conductive layer 58 and polymer should have a lowstress to provide a smooth surface and to prevent cracks and voids.Empirical testing indicates that using gold, which is malleable, for thesecond conductive layer 58 provides such a low-stress interface. Othermalleable conductive layers or metals and semiconductors that have atemperature expansion coefficient substantially similar to the polymermaterial chosen can be used as the second conductive layer 58. Thus, theactual selection of material for the second conductive layer isdependent on the choice of polymer material used to create the spacerbetween the emitter and the lens layer.

FIG. 20 illustrates the result of an etch of the second conductive layer58 to create a lens opening having a lens diameter 64. To perform theetch, a second conductive mask 62, preferably photoresist, is applied tothe surface of second conductive layer 58 and patterned to provide anopening where the second conductive layer 58 is etched. The opening isdetermined by the desired lens geometry but is preferably centered overthe emitter surface in the emitter well 68. The lens opening is alsoused to perform an etch of the polymer layer 56 thereby exposing thetunneling layer 30 on the substrate 10 surface.

FIG. 21 illustrates the result of the polymer layer 56 etch. The etch ispreferably done in DryTek 384T. Preferably the second conductive mask 62is left on the second conductive layer 58 to prevent the secondconductive layer becoming partially etched during the polymer etchprocess. During the polymer etch, the O₂ level is about 200 sccms, thepressure about 2500 mT, the power set to about 85 Watts, the He pressureset to about 10 Torr and the top temperature to about 20 C and thebottom temperature to about 12 C. The etch process takes about 135minutes to clear about 6.5 microns of resist. The etch recipe generatesabout 95 V of DC bias. The etch process balances the etch rate, etchresidue, and power to maintain as small a DC bias as possible. Thehigher the power, the faster the etch rate but more residue created. Thepower should be chosen to prevent the second conductive layer 58 fromsputtering, thus causing residue that is difficult to remove. Preferablythe resulting etch profile creates an undercut 61 that is about 1 toabout 2 microns for about each 6.5 microns of thickness of the polymerlayer 56 etched. By using a polymer etch process the etch selectivitybetween the polymer and the tunneling layer material, such as TiO_(x) ishighly selective, preferably greater than 1000:1. Empirical test resultsshow that the etch selectivity for the preferred process is about6000:1, meaning that the etch rate for polymer is about 6000Angstroms/min and the TiO_(x) is less than about 1 Angstrom/min.

FIG. 22 illustrates the application of a cathode layer 36 to the surfaceof the tunneling layer 36, sidewalls of the emitter well 68, and thesurface of the second conductive layer 58 after the second conductivemask 62 is removed. Preferably, the cathode layer 36 is deposited to athickness of about 50 to about 150 Angstroms of platinum, morepreferably about 100 Angstroms. Other materials for the cathode layer 36include iridium, gold, and tungsten just to name a few, but preferablyplatinum.

It should be noted that it would be obvious to those skilled in the artthat many variations and modifications may be made to the disclosedembodiments without substantially departing from the invention. All suchvariations and modifications are intended to be included herein withinthe scope of the present invention, as set forth in the followingclaims.

1. An electron lens for an electron emitter, comprising: a focusing lens layer; and a polymer spacer layer between the focusing lens layer and the electron emitter wherein the polymer spacer layer defining at least one opening having an undercut of about 1 micron to about 2 microns per about 6.5 microns of depth.
 2. The electron lens of claim 1 wherein the polymer spacer material is between about 2 microns and about 12 microns thick.
 3. The electron lens of claim 1 wherein the polymer spacer layer has been cured to remove volatile content.
 4. A focused electron emitter comprising the electron lens of claim
 1. 5. An electronic device comprising at least one electron lens of claim
 1. 6. A focused emitter, comprising: a tunneling layer less than about 500 angstroms in thickness disposed on a semiconductor substrate; a polymer spacer layer disposed on the semiconductor substrate and defining a first opening, havinq an undercut of about 1 micron to about 2 microns per about 6.5 microns of depth, disposed over the tunneling layer; a focusing lens layer disposed on the polymer spacer layer and defining a second opening disposed over the tunneling layer; and a cathode layer disposed on the tunneling layer.
 7. The focused emitter of claim 6 wherein the polymer spacer layer is between about 2 microns and about 12 microns thick.
 8. The focused emitter of claim 6 wherein the polymer spacer layer has been cured to remove volatile content.
 9. An electronic device comprising at least one focused emitter of claim
 6. 10. The electronic device of claim 9 wherein the electronic device is a display device.
 11. The electronic device of claim 9 wherein the electronic device is a mass storage device.
 12. A focused electron emitter, comprising: a tunneling layer less than about 500 angstroms in thickness; means for focusing electrons emitted from tunneling layer; and polymer means for spacing the means for focusing electrons from the tunneling layer wherein the polymer means has been cured to remove volatile components and defines an opening having an undercut of about 1 micron to about 2 microns per about 6.5 microns of depth.
 13. The focused electron emitter of claim 12 wherein the tunneling layer is about 100 Angstroms.
 14. The focused electron emitter of claim 12 wherein the means for focusing electrons and the polymer means for spacing have substantially the same temperature expansion coefficient. 